Process for manufacturing battery components

Abstract

The present invention pertains to a process for manufacturing a component of a secondary battery, said process comprising the following steps: (i) preparing a liquid composition comprising: a liquid medium selected from the group consisting of aliphatic ketones, cycloaliphatic ketones, cycloaliphatic esters and mixtures thereof, and at least one fluorinated polymer [polymer (F)] comprising recurring units derived from vinylidene fluoride (VDF), hexafluoropropylene (HFP) and at least one (meth)acrylic monomer (MA) having formula (I), wherein: R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, are independently selected from a hydrogen atom and a C.sub.1-C.sub.3 hydrocarbon group, and R.sub.x, is a hydrogen atom or a C.sub.1-C.sub.5 hydrocarbon moiety comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, an ester and an ether group; and (ii) processing said liquid composition to provide a film. ##STR00001##

Claims

1. A process for manufacturing a component of a secondary battery, said process comprising: (i) preparing a liquid composition, wherein the liquid composition comprises: a liquid medium selected from the group consisting of aliphatic ketones, cycloaliphatic ketones, cycloaliphatic esters and mixtures thereof, and at least one fluorinated polymer (F), wherein polymer consists of: (a) from 1.5% to 3.5% by moles of recurring units derived from hexafluoropropylene (HFP), (b) from 0.5% to 1.5% by moles of recurring units derived from at least one (meth)acrylic monomer (MA) of formula (III): ##STR00008## wherein: R.sub.1, R.sub.2 and R.sub.3 are hydrogen atoms, and R.sub.x is a hydrogen atom or a C.sub.1-C.sub.5 hydrocarbon moiety comprising at least one hydroxyl group, and (c) recurring units derived from vinylidene fluoride (VDF) in an amount that is complement to 100% by moles of total recurring units, wherein at least 8% by weight of polymer (F), based on the total volume of the liquid composition, dissolves in the liquid medium at temperatures comprised between 20 C. and 80 C.; and (ii) processing said liquid composition to provide a film.

2. The process according to claim 1, wherein at least 10% by weight of polymer (F), based on the total volume of the liquid composition, dissolves in the liquid medium at temperatures comprised between 20 C. and 80 C.

3. The process according to claim 1, wherein the liquid composition is an electrode-forming composition further comprising a powdery electrode material and, optionally, one or more additives which is processed by coating and drying a film onto a metal substrate to provide an electrode.

4. The process according to claim 1, wherein the film obtained from step (ii) is further processed by means of at least one of irradiation, film expansion, template leaching, solution precipitation techniques to provide a porous separator.

5. The process according to claim 1, wherein the film obtained from step (ii) is further processed by casting and/or melt forming to provide a dense separator.

6. The process according to claim 1, wherein the film obtained from step (ii) is further processed by coating and drying onto a separator to provide a composite separator.

7. The process according to claim 6, wherein the composite separator is obtained by coating and drying the film obtained from step (ii) onto a separator made of a polyolefin.

8. The process according to claim 7, wherein the polyolefin is selected from polyethylene, polypropylene and mixtures thereof.

9. The process according to claim 1, wherein the liquid medium is selected from acetone, methyl ethyl ketone, cyclohexanone, -butyrolactone, -valerolactone and mixtures thereof.

10. The process according to claim 1, wherein the (meth)acrylic monomer (MA) is selected from: ##STR00009## and mixtures thereof.

11. The process according to claim 1, wherein the (meth)acrylic monomer (MA) is acrylic acid or hydroxyethyl acrylate.

Description

EXAMPLE 1

a) Preparation of VDF/HFP/HEA Copolymer

(1) In a 4 lt. reactor equipped with an impeller running at a speed of 880 rpm were introduced in sequence 2455 g of demineralized water and 0.63 g of METHOCEL K100 GR suspending agent.

(2) The reactor was vented and pressurized with nitrogen to 1 bar, then 8.55 g of a 75% by volume solution of t-amyl perpivalate initiator in isododecane were introduced into the reactor, followed by 107 g of HFP monomer and 947 g of VDF monomer. The reactor was then gradually heated to 52 C. to a final pressure of 110 bar. Temperature was maintained constant at 55 C. throughout the whole trial. Pressure was maintained constant at 110 bar throughout the whole trial by feeding a 19.96 g/l aqueous solution of hydroxyethyl acrylate (HEA) monomer to a total of 709 ml. After 510 minutes the polymerization run was stopped by degassing the suspension until reaching atmospheric pressure. The polymer so obtained was then recovered, washed with demineralised water and oven-dried at 50 C. (814 g).

(3) The polymer so obtained contained 2.3% by moles of HFP and 1.0% by moles of HEA, as determined by NMR. The polymer had a melting point of 157.7 C., as measured according to ASTM D 3418 at a heating rate of 10 C./min, and a melt flow index of 5.1 g/10 min, as measured according to ASTM D 1238 (230 C., 5 Kg).

b) Preparation of a Liquid Composition of VDF/HFP/HEA Copolymer

(4) The polymer was dissolved in the liquid medium under magnetic stirring at 23 C. until complete dissolution occurred and a clear single phase solution was obtained. The upper limit to which the VDF/HFP/HEA copolymer was dissolved in acetone to advantageously yield a homogeneous solution was 15% weight/volume at 23 C.

(5) Homogeneous solutions were also obtained by dissolving the VDF/HFP/HEA copolymer in a liquid medium selected from methyl ethyl ketone, cyclohexanone, -butyrolactone and -valerolactone in an amount of 10% weight/volume at 45 C.

EXAMPLE 2

a) Preparation of VDF/HFP/AA Copolymer

(6) In a 4 lt. reactor equipped with an impeller running at a speed of 880 rpm were introduced in sequence 2460 g of demineralized water and 0.63 g of METHOCEL K100 GR suspending agent.

(7) The reactor was vented and pressurized with nitrogen to 1 bar, then 9.98 g of a 75% by volume solution of t-amyl perpivalate initiator in isododecane and 5.35 g of diethyl carbonate were introduced into the reactor, followed by 0.5 g of acrylic acid (AA) monomer, 107 g of HFP monomer and 949 g of VDF monomer. The reactor was then gradually heated to 55 C. to a final pressure of 110 bar. Temperature was maintained constant at 55 C. throughout the whole trial. Pressure was maintained constant at 110 bar throughout the whole trial by feeding a 17.44 g/l aqueous solution of AA monomer to a total of 750 ml. After 516 minutes the polymerization run was stopped by degassing the suspension until reaching atmospheric pressure. The polymer so obtained was then recovered, washed with demineralised water and oven-dried at 50 C. (852 g).

(8) The polymer so obtained contained 2.5% by moles of HFP and 1.0% by moles of AA, as determined by NMR. The polymer had a melting point of 152.4 C., as measured according to ASTM D 3418 at a heating rate of 10 C./min, and a melt flow index of 2.7 g/10 min, as measured according to ASTM D 1238 (230 C., 5 Kg).

b) Preparation of a Liquid Composition of VDF/HFP/AA Copolymer

(9) The polymer was dissolved in the liquid medium under magnetic stirring at 23 C. until complete dissolution occurred and a clear single phase solution was obtained. The upper limit to which the VDF/HFP/AA copolymer was dissolved in acetone to advantageously yield a homogeneous solution was 15% weight/volume at 23 C.

(10) Homogeneous solutions were also obtained by dissolving the VDF/HFP/AA copolymer in a liquid medium selected from methyl ethyl ketone, cyclohexanone, -butyrolactone and -valerolactone in an amount of 10% weight/volume at 45 C.

Comparative Example 1

a) Preparation of VDF/AA Copolymer

(11) The same procedure as detailed under Example 2 was followed, but without HFP monomer.

(12) The polymer so obtained contained 1.0% by moles of AA, as determined by NMR. The polymer had a melting point of 162.0 C., as measured according to ASTM D 3418 at a heating rate of 10 C./min.

b) Preparation of a Liquid Composition of VDF/AA Copolymer

(13) The polymer was partially dissolved in acetone under magnetic stirring at 23 C. Solubility of VDF/AA copolymer in acetone was 5% by weight at 23 C.

(14) It has been thus found that homogeneous solutions of at least one polymer (F) are successfully obtained, wherein the polymer (F) according to Examples 1 and 2 of the present invention was advantageously dissolved in acetone in an amount of up to 15% weight/volume at 23 C., as compared with the VDF/AA polymer according to comparative Example 1 which was partially dissolved in acetone in an amount of up to 5% weight/volume at 23 C.

EXAMPLE 3MANUFACTURE OF ELECTRODES

(15) A cathode was prepared by using a 10% weight/volume solution in acetone of a VDF/HFP/AA polymer obtained following the procedure as detailed under Example 2-a) of the invention but without diethyl carbonate. The polymer so obtained contained 2.5% by moles of HFP and 1.0% by moles of AA, as determined by NMR. The polymer had a melting point of 149 C., as measured according to ASTM D 3418 at a heating rate of 10 C./min, and an intrinsic viscosity of about 3.3 dl/g.

(16) The solution was prepared under mechanical stirring at room temperature using a Dispermat equipped with a flat PTFE disc. Conductive carbon black and Lithium Cobaltum Oxide (LiCoO.sub.2) were then added thereto under moderate stirring so that a slurry was obtained at 40% of solids concentration in which the amounts of polymer (F), carbon black and LiCoO.sub.2 were 5%, 5% and 90% by weight, respectively.

(17) The slurry was thoroughly mixed to ensure a good homogeneity. All the materials involved in the slurry preparation were either dried using molecular sieve of 4 (for the solvents) or dried for one night at 100 C. (for the powders).

(18) The slurry was then degassed under vacuum and spread using a Doctor Blade coating instrument on an Aluminum foil, previously degreased. The coating was finally dried in a vacuum oven at the fixed temperature for enough time to ensure solvent removal, typically: 15 min at 130 C., 30 min at 80 C., and 4 hours at 40 C. The thickness of the dried coating was about 50 m.

Comparative Example 2Manufacture of Electrodes

(19) The same procedure as detailed under Example 3 of the invention was followed but using a 10% weight/volume solution in N-methyl-2-pyrrolidone of polyvinylidene fluoride (PVDF).

(20) It has been found that good adhesion properties of electrodes prepared from solutions in acetone of a polymer (F) according to the invention were obtained as compared with those prepared from solutions of PVDF in N-methyl-2-pyrrolidone (see Table 1 here below).

(21) TABLE-US-00001 TABLE 1 Adhesion [N/cm] Example 3 1.2 C. Example 2 1.3

EXAMPLE 4MANUFACTURE OF POROUS SEPARATORS

(22) Two porous separators were prepared by using 2% weight/volume solutions in acetone of the VDF/HFP/HEA polymer obtained according to Example 1 of the invention and of the VDF/HFP/AA polymer obtained according to Example 2 of the invention.

(23) To these solutions were added water in an amount of 7.5% by weight, then SiO.sub.2 in a weight ratio of 1:10 (SiO.sub.2:polymer (F)). The solutions were then cast in the form of a thin film and left at room temperature until acetone was completely evaporated. The porous films so obtained having a thickness of about 20 m were washed with ethanol and dried at 60 C. for two hours.

(24) It has been found that good ionic conductivity values of porous separators prepared from solutions in acetone of the polymers (F) obtained according to Examples 1 and 2 of the invention were obtained (see Table 2 here below).

(25) TABLE-US-00002 TABLE 2 Ionic conductivity [S/cm] Example 4 Polymer (F) of Example 1: 1.3 10.sup.3 Polymer (F) of Example 2: 1.1 10.sup.3

(26) In view of the above, films obtained by processing a liquid composition according to the process of the invention were found to be suitable for the manufacture of electrodes and/or separators for use in secondary batteries.